#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(ri,n) for(int ri = (int)(n-1); ri >= 0; ri--)
#define rep2(i,x,n) for(int i = (int)(x); i < (int)(n); i++)
#define rrep2(ri,x,n) for(int ri = (int)(n-1); ri >= (int)(x); ri--)
#define repit(itr,x) for(auto itr = x.begin(); itr != x.end(); itr++)
#define rrepit(ritr,x) for(auto ritr = x.rbegin(); ritr != x.rend(); ritr++)
#define ALL(x) x.begin(), x.end()
using ll = long long;
using namespace std;

const int mod = 12;

int main(){
  int n;
  cin >> n;
  set<int> se;
  rep(i, n){
    int in;
    cin >> in;
    se.insert(in);
  }
  int ans = -1;
  rep(i, 12){
    set<int> x;
    int in;
    in = i % mod;
    x.insert(in);
    in = (i+2) % mod;
    x.insert(in);
    in = (i+4) % mod;
    x.insert(in);
    in = (i+5) % mod;
    x.insert(in);
    in = (i+7) % mod;
    x.insert(in);
    in = (i+9) % mod;
    x.insert(in);
    in = (i+11) % mod;
    x.insert(in);
    bool f = false;
    for(auto j : se){
      if(x.count(j) == 0) f = true;
    }
    if(f == false){
      if(ans == -1) ans = i;
      else ans = -2;
    }
  }
  if(ans == -1 || ans == -2) cout << -1 << endl;
  else cout << ans << endl;
  return 0;
}